Field of the Invention
The present invention relates to a process for producing non-directional electrical steel sheets free from ridging, more particularly a method of continuous casting steel slabs suitable for producing non-directional electrical steel sheets free from ridging in which the molten steel is stirred by an electromagnetic force during the casting operation so as to improve the solidification structure at a specific zone of the slab central portion.
In recent years, the development of production techniques of non-directional electrical steel sheets has been very remarkable, and high-quality electrical steel sheets can now be produced thanks to improved methods for adjustment of the molten steel composition, progress in ingot-making techniques and improved production techniques for electrical steel sheets.
However, although the introduction of new and improved techniques as above possesses the advantage that high-quality electrical steel sheets can be obtained, it also has brought in new defects. Thus, in the production of non-directional electrical steel sheets, when molten steel having adjusted composition is cast into slabs by continuous casting and such continuous casting slabs are given various workings, vertical stripes continue in the rolling direction, or so-called "ridging" appears on the steel sheets. The vertical stripes, or "ridging" deteriorate the surface appearance and commercial value of the sheets, and it is unavoidable that the space factors, etc. are lowered when such defective sheets are formed into layer-built iron cores, etc.
As for the causes for the ridging, various hypotheses have been advocated in connection with stainless steel sheets, but there has been established no definite theory, and this is true also in case of electrical steel sheets.
Various studies and experiments have been conducted by the present inventors for the purpose of clarifying the causes of the ridging, and it has been found that large elongated grains which are formed during the hot rolling and cannot be recrystallized thereafter cause the ridging and that the formation of these large elongated grains depends on the cast structure.
Descriptions will be made by referring to the attached drawings.